Screens of Carbon and Yttrium, and Screening for Silver

What's Hot in July/August 2011

by John Emsley

There are no indium mines on this planet, and yet indium tin oxide (ITO) is needed for solar cells, flat panel displays, and touch sensors. ITO combines three essential features: it is transparent, it conducts electricity, and it sticks to glass. However, its cost is rising as demand increases while supplies are limited.

Graphite is not so limited, of course, but it has only one of ITO’s benefits: it conducts electricity. Otherwise it is black, weak, and lacks stickability; indeed, it is used as lubricant. Transforming these unwanted features into a transparent material that can act as an electrode has motivated a great deal of research into graphite chemistry—witness the predominance of graphene papers in the current Hot Ten.

Among these is a new one at #10. Reporting the collective work of 16 scientists based at various institutions in Korea, Singapore, and Japan, the paper reveals a method of mass producing 30-inch wide (76 cm) graphene films and how these can be used to make a flexible touch-screen device built from transparent plastic.

The team, led by Byung Hee Hong of Sungkyunkwan University, Suwon, Korea, developed a multi-stage process. The first step was to grow a single-layer graphene film on a copper support inside a quartz tube. There it was heated under vacuum at 1,000 °C and then exposed to methane and hydrogen gases at a controlled rate, and these generated the film of graphene on its surface.
This was then transferred from the copper substrate to a layer of polymer support, referred to as "thermal release tape," by pressing the two together between rollers as in newspaper printing. The copper layer was next dissolved away electrochemically using a solution of sodium persulfate.

Touch screen, image from the Wiki Commons.
A touch screen, from the Wiki Commons.

Finally the graphene was transferred from the tape to the target substrate, which was a sheet of polyethylene terephthalate (PET), by passing the two through another pair of heated rollers at 120 °C. The resulting product met the requirements of strong adhesion, transparency, and conductivity, and it was tested as a touch-screen panel and shown to be remarkably robust despite being bendable.

Below the Hot Ten list are two papers devoted to other aspects of chemistry. At #14 is a paper from a group led by Xiaogang Liu, National University of Singapore (F. Wang, et al., Nature, 463[7284]: 1061-5, 2010; 15 citations this period, 43 total.) This paper reports a method of fine tuning sodium yttrium fluoride (NaYF4) crystals with the lanthanide elements ytterbium and erbium, and thereby controlling exactly their size, crystal form, and color emission. The resulting materials are seen as having potential applications, especially for magnetic resonance imaging.

Another paper devoted to tiny particles is at #16; this also originates from the National University of Singapore (P.V. AshaRani, et al., ACS Nano, 3[2]: 279-90, 2009; 13 citations this period, 87 total). The paper—the work of a team led by Suresh Valiyaveettil—reports on the toxicity of silver nanoparticles (a.k.a. Ag-np) in human cells. It has long been known that silver is a powerful anti-microbial agent, and silver-containing materials are used in hospitals for wound dressings and catheters. The element is now being added to household products, and there are even socks and underclothes for athletes that contain silver in the form of embedded Ag-np. But is Ag-np safe? That was the issue addressed by Valiyaveettil. The answer, given in #16, appears to be less than reassuring.

The genotoxicity (gene damage) and the cytotoxicity (cell death) of nanosilver were the focus of the research, and the form of silver used was starch-coated nanoparticles. The targeted tissue was normal human fibroblast cells, which are involved in connective tissue, and human glioblastoma cells, which are one of the more malignant forms of brain tumor.

The conclusion of the paper is that nanoparticle silver, even in small doses, adversely affected the mitochondria of the cell, leading to DNA damage and chromosome errors, although some of this was repairable. With respect to cancerous cells, it was noted that while Ag-np could delay their proliferation, it could also have the same effect on normal cells. The authors conclude their paper with a not-unexpected observation that more research needs to be done.End

Dr. John Emsley is based at the Department of Chemistry, Cambridge University, U.K.

 
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What's Hot in Chemistry
Rank Paper Cites This Period
Jan-Feb 11
Rank Last Period
Nov-Dec 10
Y.Y. Liang, et al., "For the bright future—Bulk heterojunction polymer solar cells with power conversion efficiency of 7.4%," Adv. Materials, 22(20): E135-8, 25 May 2010.  [U. Chicago, IL; Solarmer Energy Inc., El Monte, CA]   *612IK 36 3
D.V. Kosynkin, et al., "Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons," Nature, 458(7240): 872-6, 16 April 2009.  [Rice U., Houston, TX] *433CS 30 6
3 X.S. Li, et al., "Large-area synthesis of high-quality and uniform graphene films on copper foils," Science, 324(5932): 1312-4, 5 June 2009. [U. Texas, Austin; Texas Instruments, Dallas]     *453TF 27 1
L.Y. Jiao, et al., "Narrow graphene nanoribbons from carbon nanotubes," Nature, 458(7240): 877-80, 16 April 2009. [Stanford U., CA] *433CS 24 8
J.H. Hou, et al., "Synthesis, characterization, and photovoltaic properties of a low band gap polymer based on silole-containing polythiophenes and 2,1,3-benzothiadiazole," J. Am. Chem. Soc., 130(48): 16144-5, 3 December 2008. [U. Calif., Los Angeles; Solarmer Energy Inc., El Monte, CA]   *406UG 22
6 Y.Y. Liang, et al., "Highly efficient solar cell polymers developed via fine-tuning of structural and electronic properties," J. Am. Chem. Soc., 131(22): 7792-9, 10 June 1009. [U. Chicago, IL; Solarmer Energy Inc., El Monte, CA]   *460HD 20 5
7 F.C. Krebs, T. Tromholt, M. Jorgensen, "Upscaling of polymer solar cell fabrication using full roll-to-roll processing," Nanoscale, 2(6): 873-86, June 2010. [Tech. U. Denmark, Roskilde]  *608ML 20
B. Lim, et al., "Pd-Pt bimetallic nanodendrites with high activity for oxygen reduction," Science, 324(5932): 1302-5, 5 June 2009.  [Washington U., St. Louis, MO; Brookhaven Natl. Lab., Upton, NY]  *453TF 19 7
9 Y.Y. Liang, et al., "Development of new semiconducting polymers for high performance solar cells," J. Am. Chem. Soc., 131(1): 56-7, 14 January 2009.  [U. Chicago, IL; Solarmer  Energy Inc., El Monte, CA]  *394WF 18
10 S. Bae, et al., "Roll-to-roll production of 30-inch graphene films for transparent electrodes," Nature Nanotech., 5(8): 574-8, August 2010.  [8 South Korean, Singaporean, and Japanese institutions]  *635BZ 17
SOURCE: Thomson Reuters Hot Papers Database. Read the Legend.

 

 

 

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